[flang] Spelling and format edits to README.txt. NFC.

flang/README.md

@@ -159,7 +159,7 @@ make test check-all
 
 To run individual regression tests llvm-lit needs to know the lit
 configuration for flang. The parameters in charge of this are:
-flang_site_config and flang_config. And they can be set as shown bellow:
+flang_site_config and flang_config. And they can be set as shown below:
 ```
 <path-to-llvm-lit>/llvm-lit \
  --param flang_site_config=<path-to-flang-build>/test-lit/lit.site.cfg.py \
@@ -214,9 +214,11 @@ To generate doxygen-style documentation from source code
 cd ~/llvm-project/build
 cmake -DLLVM_ENABLE_DOXYGEN=ON -DFLANG_INCLUDE_DOCS=ON ../llvm
 make doxygen-flang
+```
 
 It will generate html in
 
+```
     <build-dir>/tools/flang/docs/doxygen/html # for flang docs
 ```
 ## Generate Sphinx-based Documentation
@@ -227,17 +229,18 @@ is mostly meant to be processed by the Sphinx documentation generation
 system to create HTML pages which would be hosted on the webpage of flang and
 updated periodically.
 
-If you would like to generate and view the HTML locally, install
-Sphinx <http://sphinx-doc.org/> and then:
-
+If you would like to generate and view the HTML locally:
+- Install [Sphinx](http://sphinx-doc.org/), including the [sphinx-markdown-tables](https://pypi.org/project/sphinx-markdown-tables/) extension.
 - Pass `-DLLVM_ENABLE_SPHINX=ON -DSPHINX_WARNINGS_AS_ERRORS=OFF` to the cmake command.
 
 ```
 cd ~/llvm-project/build
 cmake -DLLVM_ENABLE_SPHINX=ON -DSPHINX_WARNINGS_AS_ERRORS=OFF ../llvm
 make docs-flang-html
+```
 
 It will generate html in
 
+```
    $BROWSER <build-dir>/tools/flang/docs/html/
 ```